Complementary Metal Oxide Semiconductor (CMOS) image sensors have come to dominate the image sensor marketplace for numerous applications because of the areas of integration, power consumption/dissipation and total system size. CMOS image sensors are used for applications including, for example, camera phones, security cameras, PC video capture, barcode scanners, fax machines, desk-top scanners, toys, biometric devices and the like.
Three useful features found in many charge coupled device (CCD) images sensors are global shutter mode, pipeline shutter mode and binning. In a global shutter mode of operation, the pixels are reset before integration. The pixels are allowed to accumulate charge during an integration (“exposure”) time. At the end of the integration time, the accumulated charge from each pixel is transferred to a storage area. Then the signals are read out from the storage area. Since the pixels are reset at the same time, integrate over the same time interval, and are transferred to the storage area at the same time, the global shutter mode may diminish motion artifacts compared to some other electronic shutter modes.
The term “pipeline” or “pipeline shutter” is generally understood to describe or refer to an electronic shutter mode in which a pixel accumulates light energy and transfers its charge to a memory element associated with the pixel. While the pixel's memory element is being read, the pixel's integrating element is accumulating light. In this manner, pixels are almost constantly “exposed,” have a higher refresh rate and produce more images or “frames per second.” A pipeline shutter mode maybe well suited to high speed image capture.
Binning is generally understood to describe or refer to a method of combining the output of individual pixels in the charge domain, as opposed to combining in the voltage domain. Binning generally produces enhanced low-light operation with reduced noise effects, in comparison to other techniques.